Physiologia Epicuro-Gassendo-Charltoniana, or, A fabrick of science natural, upon the hypothesis of atoms founded by Epicurus repaired [by] Petrus Gassendus ; augmented [by] Walter Charleton ...

CHAP. V. THE NATURE OF LIGHT.

SECT. I.

IN our three immediately praecedent Chapters, we have often mentioned the RAYES OF LIGHT, as the Material Principle both of all Visible Species, and Colours; and that we may not leave our Reader unsatisfied in any particular, the communication whereof seems necessary, or advan∣tageous to His full comprehension of all our Conceptions relating to those Arguments, or any other of Affinity to them, that may hereafter occurr: we judge it our Duty, here to let him clearly know, What No∣tion we have of the Nature of that so admirably glorious and universally comfortable an Entitie, Light.

By the Rayes of Light, we understand, certain most tenuious streams of Igneous Particles in a continued fluor, and with ineffable pernicity succeding each other in direct lines, either immediately from their Lucid Fountain, or mediately from solid bodies reflecting them, towards the eye, and sensibly affecting the same.

This Description may receive somewhat more both of perspicuity and credit, if we consider the parallelism, or analogy, that each distinct Ray of Light holds to a stream of water, exsilient from the Cock of a Cistern, or tube of an Arti••icial Fountain. For, the reason why a stream of water issues from a tube in a kind of arch, and flows to some distance from its source

through the aer; is only this, that the particles of Water first exsilient, upon the remove of the stopple or obstacle, are so closely and contiguously pursued by other particles immediately following, and those again by others indesinently emanant, that they are impelled forward and driven on with such rapidity, as overcomes their natural propensity to direct descent, by reason of their Gravity, and carries them in a tense line from the vent so long as their impulse is superior to that of their Gravity; which encreasing more and more in each degree of distance, doth at length become victor over the force of the Motion, and praecipitate them downright. And as this gradual Tensity, or Rigidity of a stream of Water ariseth to it only from the Pressure or impulse of the Antecedent particles by the Conse∣quent, in an uninterrupted succession: so may we conceeve, that a Ray of Light, or Wand (many of our Modern and most discovering Philoso∣phers call a stream of Light, Virgula Lucis; and that by an unstrained Metaphor.) consisting of many rayes seemingly united, such as we ob∣serve shining in a room through some hole in the Window, or other in∣let; doth therefore become in a manner Tense, or Direct, only because the particles first emanant from the Lucid Fountain are so urged and prest on by the subsequent, and those again by others, with equal pernicity, that they cannot deflect from a direct line, or obey the inclination of their Gravity, until some solid Body, interposed, cut off the fluor, by interrupting the succession, and then the Tensity, or Pressure ceasing, the Particles become incontiguous and disappear: as is observable, upon closing the inlet, through which a stream of Light is admitted into an otherwise ••pace room. For, immediately the successive supply of luminous particles being intercepted, the Antecedent droop, fail, and surrender that part of space, which they possest with splendour sufficient to affect the sense, to the horrid encroachment of Darkness.

This full Comparison praemised, we shall comply with opportunity, and here concisely observe

(1) That Aquilonius, and most other Opticomathematicians do excel∣lently distinguish Light into so many gradual Differences, as are the Refle∣ctions of which it is capable; denominating that Light, Primary, whereby a Body is immediately, or in direct lines from the Lucid Fountain, illustra∣ted; that Secondary, which reflected from one solid body, illuminates a••other; that a Third Light, which illuminateth a body, after two Reflecti∣ons from others: and so forward up to the Centenary, and Millenary light, if, at least, it be capable of so many reflections, from bodies most solid and polite.

(2) That Light at Second hand is more weak than at First; at Third than at Second; at Fourth than at Third, &c. or, that Light becomes so much Weaker, by how many more Reflections it hath suffered. Not (as is vulgarly concluded) that a Reflex ray is less Tense, or the successive pres∣sure of its particles less violent or rapid, than those of a Direct; for, the motion of Light, however frequently reflected, is incomprehensibly swift: but, that every reflection doth much diminish it, some rayes being always diverted and scattered into other parts of the medium, by reason of the Asperity, or Inaequality of the particles in every superfice; and so there being no superfice that remits in a direct line the full number of rayes

(some have adventured to say, scarce half so many as) it received, and con∣sequently the eye receiving fewer and fewer rayes successively from every Reflectent, must be more weakly affected and moved by the thin remain∣der. For, if all the rayes of the Sun directly incident on a Wall, were thence reflected on another wall situate at a right angle; the Second wall would be fully as luminous as the First; and consequently, the Secondary light would be as strong and resplendent as the Primary: but, since the superfice of the First Wall is unequal and scabrous, it must of necessity come to pass, that though many of the rayes incident thereon are from thence projected on the Second, yet as many are repercussed into other re∣gions of the Medium, some upward, others downward; some to the right hand, others to the left, &c. according to the various faces, or sides of the small particles, with asperity contexed in the superfice of each stone there∣in. So that one half, if not the major part of the directly incident rayes being diverted from the Second Wall, the Light thereon appearing must be proportionately less strong and fulgent, than that, which illuminates the First. By the same reason, if the Second Wall by reverberation derive the Light to a Third; it must likewise play the Publican, and remit but half so many rayes, as it received from the First: and so must the Third transmit a thinner stock of light to a Fourth, and a Fourth to a Fifth, &c.

If this Example seem scarce praegnant enough, let us descend into a deep Pit, or with the Troglodites creep into the bowels of some subterraneous Cavern, and there our sense will demonstrate, that multiplied Reflections of Light gradually diminish it even to absolute insensibility. For, the rayes of the Sun falling into the aperture of either Mine, or long Cave, are by ob∣lique repercussions from their sides conveyed inwards, and so often bandied from side to side, that few or none attain to the bottom to diminish the opa∣city thereof: every reflection remitting some rayes, more or less, toward the mouth of the pit, or cave. And this ushers in our Third obser∣vable.

(3) That Aristotles assertion, Lumen esse in continuo motu, that Light is in perpetual motion, or reverberated to infinity; is profound and ortho∣dox. For, notwithstanding the illusion of our sense persuades us, that all things in the aer about us, and within our houses, are calm and unmoved: yet doth that better Criterion, our Reason, assure that the Light diffused through the aer is in perpetual inquietude, and consisteth of nothing else but a most tenuious Contexture of innumerable rayes, swarming from and to all regions uncessantly, so long as the Lucidum ceaseth not to maintain the succession of fresh rayes, that may be reflected from all obvious bodies. So that in what ever part of the medium the eye is posited; it shall ever have some object or other praesented: and particularly that, from whence some rayes are more directly reflected into its Pupil. Not that we con∣ceive the Light diffused through the whole aer to be Continued, or United in all points, as are the parts of Water in the Sea: but, that, as a Spiders Web appears to be one entire and united body, though it consist of distinct Filaments, variously intricate, and mutually decussating each other; so also is Light, Non unum quid Simplicissimum, sed Compositissimum, some one thing not most Simple or consisting of parts continuedly united, but most Compound, or consisting of parts so interwoven as to exclude all sensible

discontinuity; though our sense deprehend it to be Incompositissimum▪ because the acies of the sight is too blunt to discern the single rayes, which like most slender Filaments with exquisite subtilty interwoven into a visible invisible Web, replenish the whole Medium.

(4) That, though Light be ever debilitated by Reflection, yet is it ma∣ny time Corroborated by Refraction; as that transmitted through Convex Glasses, and Glass Vials replete with limpid water: and then only debilita∣ted, when it is Refracted by a Concave superficies of a pellucid body, or after refraction on a Plane superfice, is lookt upon obliquely. For as no reason can be given for the Debilitation of Light by Reflection; but the Attenuation or Dimmution of the number of its Rayes: so can none be assigned for the Corroboration of it by Refraction in a Convex Glass, or Vial filled with clear water; but the multiplication of its Rayes, in some part of the Medium. Nor is there, on the contrary, why we should con∣ceive Light to be made weaker by some Refraction, unless in this respect only; that if it had not fallen foul of a Refringent body, a greater number of rayes would have continued their direct progress in a closer order, or more united stream: and so their Debility depends meerly on their Disgregati∣on; not Diminution of Pernicity. Certainly, that Light which is corro∣borated by refraction in a Convex Glass, would be yet more strong and energytical, if all those Rayes, that strike upon the obverted side of the Glass, were so refracted, as to permeate and unite in the aer beyond the averted side thereof: and those rayes which are trajected through the bot∣tome of a Glass Vial filled with water, arrive at the eye so much the more Disgregate, by how much the more obliquely the eye is posited; because the water being in the bottom more copious, and so containing more retun∣dent particles, doth divert the greatest number of them into the ambient. And hence we inferr, that if the beams of the Sun be conceded more weak in the Morn and Evening than at Noon, only because of a greater Refra∣ction by more vapours then interposed; that effect must chiefly arise from hence, that the Rayes come unto us obliquely, after their trajection through those swarms of denser vapours, and consequently more Dissipated, the major part of them being diverted into other regions of the Medium. Moreover, insomuch as all Masters in the Optiques clearly demonstrate that the Image of an illustrate object, speculated through water in the bot∣tome of a vessel indiaphanous, doth appear less lively to those, that look on it obliquely, than to those that behold it in direct lines respective to the tendency of the Light refracted by the Water; and that the superfice of every object hath so much the fewer parts discernable, by how much more obliquely it is speculated: therefore is it purely necessary, that the Image of an object appear more Contracted, when speculated by a Vertical line, than when exhibited to the eye in a direct, and Irrefracted one. And this also we judge to be in some part the Cause, why the Sun when nearest to our Horizon, either Orient or Occident, appears in a Figure more Ellipti∣cal or Oval, than Sphaerical: for then do we behold it per lineam Verti∣calem. We say, in part; because the same Effect may also be induced by the Form of the Vaporous Sphaere. However this may be controverted, yet most certain it is, that the Lucid Image of the Sun is alwayes more Vi∣tiated, when it arrives at our ••ight from an Humble position, than a sublime or Meridional: Non quod pauciores quidem radij Directi mane, quàm meri∣die; sed ••eflexi tamen pauciores, qui cum illis misceantur, ipsorum{que} Vim

augeant. Quia Directi supra liberam horizontis planitiem praetereant, nec redeant; cum sub meridiem in terram impacti non resilire regredique non va∣leant; as Gassendus, in Epist. ad Bullialdum, de Apparent. Magnitud. Solis Humilis & sublimis. And this hath a near relation to our fifth obser∣vable.

(5) That the Body from which the rayes of a Lucid object more emi∣nently the Sun, are repercussed so as to diminish the shadow round about it, seems not to be the Conterminous Aer, but rather some Opacum con∣stitute beyond both it and the Aer. Not that we deny the necessary re∣flection of many of the Luminous rayes proceeding from the Sun, by those myriads of myriads of particles floating in the Atmosphere; and so the remission of them back again toward their source, and the consequent diminution of the shadow invironing the same: but that we conceive the proportion of rayes so diverted, to be so small, as to be much below the observation of our sense. For, He that is in the bottom of a deep Mine, hath his sight so little advantaged by the Aer illuminated by the me∣ridian beams of the Sun, that though he can clearly behold the Starrs in the Firmament, immensely beyond that vast tract of Aer then illustrate; yet can he hardly perceive his own hand, or ought else about him, since all the rayes of Light, which affect his eyes, are only those few that have escaped repercussion upward, by those many oblique refractions in the sides of the Mine. Thus also in the night are we no whit relieved by the aer, or Aether surrunding our Horizon, or more properly, our Hemisphere beyond that region, to which the Cone of the Earths shadow extends: though the Sun doth as freely and copiously diffuse its light through all that vast Ocean of Aer, or Aether beyond the extent of the Earths shadow, at our Midnight, or when it is Vertical to the Antipodes, as at our noon when it is Vertical to us: which could not be, if any sensible proportion of light were reflected toward us by the particles of the Aer, or Aether, replenishing the subcae∣lestial space. Hence comes it, that what Light remains to our Hemisphere in the night, ought to be referred, not to any Reflection of the Suns rayes from the sublime aer, or Aether; but to the Stars, or Moon, or both. And this is also no contemptible argument, that the Concave of the Firmament is Opace, and not azure, as most suppose.

(6) That every Lucid Bodie is considerable in a double capacity; (1) Qua Lucidum, as shining with either native, or borrowed light, it illuminateth other bodies: (2) Qua Visibile, as it emits the visible Image of it self. In the First Respect, we may conceive it to be the Center, from which all its luminous Rayes are emitted by Diffusion Sphaerical, according to that esta∣blisht maxime of Alhazen, Omne punctum luminosum radiare sphaeralitèr: in the Second, we may understand it to emit rayes in a diffusion Pyramidal, the base whereof is in it self, and cone in the eye of the Spectator. For, particularizing in the Sun, which being both a Lucid Body and a Visible ob∣ject, falls under each acceptation; we must admit the Rayes thereof illumi∣nating that vast ocean of Space circumscribed by the concave of the Heavens, to be deradiated from it sphaerically, as so many lines drawn from one common Centre; because they are diffused throughout a region far greater than the Sun it self: and those rayes, that Constitute the Visible Images of it, stream from it in Cones or pyramids; because they are ter∣minated in the pupil of the beholders eye, a body by almost infinite degrees

less than it self. This is fully demonstrated by the Forms of Eclipses, which no man can describe but by assuming the Sun as the Base, from whose Extremes myriads of Rayes emanant, and in their progress circu∣larly environing the Margin of the Earth, or Moon, pass on beyond them till they end in a perfect Cone; the Orbs of the Earth and Moon being by many degrees less in circumference, than that of the Sun. This confirms us, that those Optico-mathematicians are in the centre of truth, who teach, that the rayes of the Sun, and all other luminous Objects as they consti∣tute its visible species, are darted only Pyramidally; insomuch as they are received in the eye of each Spectator, so much less than the Sun, or other Luminary: but that they progress in a sphaerical Diffusion, in respect of the circumambient Aer, in each point whereof the Luminary or Lu∣cidum is Visible. Since, should we allow the Concave of the Firmament to be as thickly set with eyes, as Joves vigilant Pandars head was imagined by Poets; we could not comprehend how the orb of the Sun could be discernable by them all, unless by conceding this sphaerical diffusion of Py∣ramids to all parts of the same. And this doth as well illustrate as confirm a former Antiperipatetical Paradox of ours, that the visible Species of an object is neither total in the totall Space, nor total in every part there∣of; but the General Image is in the whole Medium, and the Partial or Particular Images, whose Aggregate makes the General Image, in the sin∣gular parts of the Medium: because no singular eye from any singular part of the Medium, can perceive the whole of the object, but those parts on∣ly, which are directly obverted to that part of the Medium, in which the eye is posited. Which assertion we inferred from hence, that not only the whole, but also every sensible particle of an object doth emit certain most subtile rayes, constituting the species of it self, in a sphaerical diffusion, so that the various particles emit various rayes, that variously decussate and intersect each other, in all parts of the Medium: and as these rayes are emitted sphaerically, ex se▪ according to that maxime, Omne Visibile sui spe∣ciem effundere sphaeraliter; so do most of them, ex Accidente, convene in their progress, and so reciprocally intersect, as to fulfill the figure of a Py∣ramid. Whence it naturally follows, that because some Rayes must con∣vene, in all parts of the Medium, in this manner; therefore are Pyramids of rayes made in all points of the Medium, from whence the object diffu∣sing them is visible. Notwithstanding this, we shall so farr comply with the Vulgar doctrine, as to allow; that in respect even of one single eye, in whatever part of the Medium posited, the diffusion of rayes from an ob∣ject may be affirmed to be Sphaerical: insomuch as no part in the object at considerable distance singly discernable, can be assigned, which is not less than the pupil of the Eye.

(7) That the Light diffused through the Medium, is not seen by us: but that thing beyond the Medium from which some rayes are ultimate∣ly reflected into the eye. For, if it chance that we persuade our selves, that we perceive something in the Medium; it is not pure Light it self, but some crass substance, the small particles of Dust, Vapours, Smoak, or the like, which having received light from some luminous source, reflect the same toward the eye.

SECT. II.

NOw, of all these Praeconsiderables only the First can be judged Praecarious, by those whose Festination or Inadvertency hath not given them leave to observe the Certitude thereof inseparably connected to the evidence of all the others, by the linkes of genuine Conse∣quence. And therefore, that we may not be wanting to them, or our selves, in a matter of so much importance, as the full Confirmation of it by nervous and apodictical Reasons; especially when the Determina∣tion of that eminent and and long-lived Controversie concerning the QUIDDITY or Entity of Light, Whether it be an Accident, or Substance, a meer Quality, or a perfect Body? seems the most proper and desiderated subject of our praesent speculations, and the whole Theory of all other sensible Qualities (as Vulgar Philosophy calls them) is dependent on that one cardinal pin, since Light is the nearest allied to spiritual natures of all others, and so the most likely to be Incorporeal: we must devote this short Section to the perspicuous Eviction of the CORPORIETY of Light.

Not to insist upon the grave Authority either of Empedocles, who, as Aristotle (1. de sensu & sensili: & de Gener. Animal. 1. cap. 8.) testifieth, affirmed Light to be 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉, Effluxionem, a material Emanation, and required certain proportionate Pores, or most slender passages in all Dia∣phanous bodies, for their transition; or Plato, who defined Colour, or Light disguised, to be 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉, Ef••luentem quandam Flammulam; or of Democritus and Epicurus, both which are well known to have been grand Patrons, if not the Authors of that opinion, that Light is corporeal: we judge it alone sufficient to demonstrate the Corporiety of Light, that the Attributes thereof are such, as cannot justly be adscribed to any but a Cor∣poreal Entity.

1Such are (1) Locomotion; for manifest it is, that some substance, though most tenuious, is deradiated from every Lucidum to the eye of the distant Spectator: nor is a Bullet sent from the mouth of a full charged Cannon with the millionth part of such velocity, as are the arrows shot from the bow of Apollo; since the rayes of the Sun are transformed from one end of the heavens to the other, in a far less division of time, than a Cannon Bullet is flying to its m••••k.

2(2) Resilition; for the rayes of light are sensibly repercussed from all solid bodies, on which they are projected; and that with such pernicity or rapid motion, as transcends, by inassignable excesses, the rebound of a Can∣non Ball from a Rock of Adamant.

3(3) Refraction, for our sense confirms, that Light is ever refracted by those Bodies, which allow its rayes a passage, or through-fare, but not an absolute free and direct one.

(4) Coition, or Union, or Corroboration, from bodies either reflecting,4 or transmitting many rayes to one common point of concurse, where they become so violent as to burn any thing applied.

(5) Disgregation and Debilitation,5 from the didaction of its rayes re∣flected or trajected: so that those which before during their Union were so vigorous as to cause a conflagration, being one distracted become so lan∣guid as not to warm.

(6) Igniety; since Light seems to be both the Subject,6 and Vehicle to Heat, and those speak incorrigibly, who call Light, Flame attenuated. Which we shall less doubt, if we consider the natural Parallelism betwixt Flame and Water, Light and a Vapour. For, as Water by Rarefaction, or Attenuation becomes a Vapour; so may we conceive Flame by Attenuation to become Light circumfused in the aer: and as a Vapour is nothing else but Water so rarefied into small discontinued par∣ticles, as that it doth scarce moisten the body on which it is impacted; so is Light nothing else but Flame so dilated by Rarefaction, that it doth hard∣ly warm the body it toucheth. Lastly, as a Vapour how finely soever rarefied, is still substantially Water; because only by the Coition of its dif••used particles it returns again to Water, as in all distillations: so must we account Light however rarefied, to be still substantially Flame; because only by the Coition, or Congregation of its dispersed rayes it is reducible into absolute Flame, as in all Burning-glasses.

These Attributes of Light considered, it is not easie for the most praevaricate judgment not to confess, that Light is a Corporeal substance, and the Rayes of it most tenuious streams of subtle Bodies: since it is impossible they should be deradiated from the Lucid Fountain with such ineffable pernicity, transmitted through the Diaphanum in a mo∣ment, impacted against solid bodies, repercussed, corroborated by Unition, debilitated by Disgregation, &c. without essential Corpulency.

Notwithstanding this apodictical evidence of the Corporiety of Ligh••, the refractary Peripatetick will have it to be a meer Quality, and objects

(1) That his master Aristotle, impugning the doctrine of Demo∣critus, Epicurus, and others, who ascribed Materiality to Light, de∣fined it to be meerly 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉 perspicui, an act of the Perspicuum.

To this we answer, (1) That though Aristotle thought it sufficient barely to deny that light is 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉, ullius corporis Ef••luxum, and to affirm it to be Energian perspicui, ut perspicuum; yet will the judicious discover it to be rather an ambage to circumvent the incircumspect, than a demonstration to satisfie the curious. For, though Philopouus (2. de Anim. 7.) willing to conceal or guild over his Masters error, interpreteth his Perspicuum actu, or illustrate Nature, and so Light to be a kind of Chord, which being continuedly inter∣posed betwixt the object and the eye, causeth that the Colour thereof posited beyond the Medium, doth affect and move the eye to the act of intuition: yet hath He left the Reason and Manner of this supposed Act

of the Perspicuum on the eye, the chief thing necessary to satisfaction, involved in so many and great Difficulties, as proclaim it to be absolute∣ly inexplicable. (2) That albeit we deny not Illumination to be meer∣ly ••cc••dental to opace Bodies; yet therefore to allow the Light, where∣with they are illuminate, to be an Accident, and no Substance, is a ma∣nifest Alogie. And to affirm, that the Aer, Water, or any Diaphanous body is the subject of Inhaesion to Light, is evidently incongruous; because every Medium is simply Passive, and remains unmoved while the Light pervades it: and how can Light pervade it, if it be not Corporeal? or how can the rayes thereof conserve their Tensity and Di∣rectness in the Aer, while it is variously agitated by wind and other causes, if they were not absolutely independent thereupon? (3) What Aristotle saith concerning the Propagation of the species of Light even to infinity in all points of the Medium, besides its incomprehensibili∣ty, is absolut••ly inconsistent to the Pernicity of its motion, which is too ra∣pid and momentany to proceed from a fresh Creation of Light in every point of the medium: since the multitude of fresh productions successively made, would r••quire a far longer time for the transmission of the light of a candle to the eye of a man at the distance of but one yard, than our sense de∣monstrates to be necessary to the transmission of the light of the Sun from one end of Heaven to the other.

(2) That by allowing Light to be Corporeal, we incurr the absurd••ty of admitting two Bodies into one and the same place.

Which is soon solved by reflecting on what we have formerly and frequently said, concerning Inanity interspersed, and observing what we shall (God willing) say of those eminent Qualities, Rarity and Perspi∣cuity: from either of which it may be collected, how great a Multitude of Pores are in every Rare and Perspicuous Body, which remain tenantable, or unpossessed.

(3) That from the Corporiety of Light it must follow, that a Body ma•• be moved in an Instant. But he hath not yet proved that the motion of Light is instantaneous: and we have, that it is not, but only Momentany, i. e. that Ligh•• is moved in a certain space of time, though imperceptible, yet divisible, and not in one individual point, or Instant.

(4) That the Rayes of Light are Invisible in pure Aer, and by conse∣quence Immaterial. Solut. Their Invisibility doth not necessitate their Immateriality; for the Wind, which no man denies to be Corporeal, is invisible: and as it sufficeth that we feel the Wind in its progress through the aer, so also is it sufficient that we perceive Light, in the illumination of Opace Bodies, on which it is impinged, and from which it is reflected. Be∣sides, whoso maketh his sense the measure of Corporiety, doth strain it to a higher subtility, than the constitution of its Organs will bear, and make many more spiritual Entities, than can be found in the Uni∣verse; nay, He implicitely supposeth an Immaterial Being naturally capable of Incorporation meerly by the Unition of its dispersed par∣ticles; since many rayes of Light congregated into one stream become visible.

(5) That the Materiality of Light is repugnant to the Duration of the Sun; which could not have lasted so long, but must have, like a Tapour, ex∣hausted its whole stock of Luminous Matter, and wincked out into perpetual night, long since, if all its Rayes were substantial Emanations, according to our Assumption.

But this Refuge may be battered with either of these two shots. 1 The superlative Tenuity of the Luminous particles continu••lly emitted from the body of the Sun, is such as to prevent any sensible minoration of its orb, in many 1000 yeers. (2) If the Diametre of the Sun were minorated by 100000 miles less than it was observed in the days of Ptolomy; yet would not that so vast Decrement be sensible to our sight: since being in its Apo∣gaeum, in summer, it doth not appear one minute less in Diameter to the strictest astronomical observation, than in winter, in its Perigaeum, and yet Snellius, Bullialdus, and Gassendus, three Astronomers of the highest form, assure us that it is about 300000 miles more remote from us, in its Apogae∣um, than Perigaeum.

(6 and Lastly) That if Light were Flame, then would all Light warm at least: but there are many Lights actually Cold, such as that in the Phospher M••neralis, or Lapis Phenggites, of whose admirable Faculty of imbibing, retaining and emitting a considerable light, the excellent Fortunius Licetus hath written a singular Tract, and Athanas. Kircherus a large chapter (in Art. magn. Lucis & Umbrae lib. ••. part. 1. cap. 8.), in Gloworms, the scales and shells of some Fishes, among which the most eminent are those Dactyli mentioned by Kircher (in libri jam citati part. 1. cap. 6.) in these words, sunt & Dactyli, ostreacei generis, qui vel manibus triti lumen veluti scintillas quasdam ex se spargunt: quemadmodum Melitae, in Sicilia, Calabria, & Ligustici maris oris non sine admiratione à piscatoribus & nautis instructoribus observasse memini; in Rotten Wood, &c. Ergo, &c.

Answer, The Defect of actual Heat in these things, doth arise, in part from the abundant commistion of Gross and Viscid Humidity with those igneous Particles that are Collucent in them; but mostly from the ex∣ceeding Rarety of those Luminous Sparks: which being so thin and lan∣guid, as to disappear even at the approach of a Secondary Light, cannot be expected vigorous enough to infuse an actual warmth into the hand that toucheth them; especially when experience attesteth, that the Rayes of the Sun, after two Reflections, become so languid by Attenuation, as they can hardly affect the tenderest hand with any sensible Heat. And therefore, unless it can be evinced, that the disgregation of the parts of a Body, doth destroy the Corporiety of it; and that the simple Attenuation of Lig••t doth make it to be no Light: we ask leave to retain our p••rsuasion, that the existence of many lights, which are devoyd of Heat, as to the per∣ception of our sense, is no good Argument against the Igniety and Cor∣poriety of Light.

Notes

• Art. 1. The Clasp, or Ligament of this, to the praecedent Chapter.
• Art. 2. The Authors Notion of the Rays of Light.
• Art. 3. A Parallelism betwixt a stream of Wat••r exsilient from the Cock of a Cistern, and a Ray of Light emanant from its Lucid Fountain.
• PRAECONSI∣DERABLES.
• Art. 4. Light distin∣guisht into Primary, Secon∣dary, &c.
• Art. 5. All Light De∣bilitated by Reflection: and why.
• Art. 6. An Example, sensibly de∣monstrating the same.
• Art. 7. That light is in perpetual Motion; ac∣cording to Arist.
• Art. 8. Light, why Corroborated, in some cases, and Debilitated, in others, by Re∣fraction.
• COROLLA∣RY.

  Why the Fi∣gure of the Sun, both ri∣sing & setting, ap••ears rather Elliptical, than Sphaerical.
• Art. 9. PARADOX. That the pro∣portion of So∣lary Rayes re∣flected by the superiour Aer, or Aether, to∣ward the Earth, is so sma••l, as not to be sensible.
• Art. 10. That every Lucid Body, as Lucid, doth emit its Rayes Sph••erically: but, as Visible; Pyramidally.
• Art. 11. That Light is invisible in the pure me∣dium.
• Art. 1. The Necessity of the Authors confirmation of the F••••st Praeconsiderable
• Art. 2. The CORPO∣RIETY of Light, demon∣strated by its j••st Attributes: viz.
• 1

  Locomotion.
• 2

  Resilition.
• 3

  Refraction.
• 4

  Coition.
• 5

  Disgr••gation
• 6

  Igniety.
• Art. 3. Aristotles Defi∣nition of Ligh••, a meer Ambage, and incomprehen∣sible.
• Art. 4. The 〈◊〉〈◊〉 of Light imp••rts not the Coexi∣stence of two B••dies in one Place: contra¦ry to the Peri∣patetick.
• Art. 5. Nor the moti∣on of a B••dy to be Instanta∣ne••us.
• Art. 6. The Invisibili∣t•• of ••ight in the limpid me∣dium, no Ar∣gument of its Immateriality: as the Peripa∣tetick prae∣sumes.
• Art. 7. T••e Corporiety of Light fully consistent with the Du∣ration of the Sun: contrary to the Peripa∣tetick.
• Art. 8. The in••••nsibi∣lity of Heat in many Lucent B••die•• no va∣lid Argument against the praesent The∣sis, that Light is Flame Atte∣nuated.